1. Technical Field
The present invention relates generally to circuit design software, and more particularly, to a methodology and computer program that simultaneously routes signal and return paths to avoid referencing signals to non-optimal reference planes.
2. Description of the Related Art
As signal frequencies increase, and with a focus on reduced power and emissions, signal management within circuit boards, multi-chip module (MCMs) substrates and other package substrates has become increasingly critical. With the high frequencies and/or narrow pulse widths of critical signals in present-day digital circuits, special layout techniques are typically required for routing critical signal paths to minimize reflections, impedance mismatches and coupling between signal paths, according to electromagnetic analysis techniques. Signal return paths, which maybe reference planes such as power planes or dedicated signal planes are typically provided between signal layers to provide controlled signal path impedance and to shield overlapping signal paths from each other.
However, not all signals routed on a given layer should be referenced to a single signal reference plane. Additionally, due to cost, thickness and fabrication limitations, it is desirable to reduce the number of power planes and/or dedicated return path planes required in an interconnect system. Typically, designs may be compromised by having to route signals through reference planes, which can split the reference planes so that they do not properly reference signals that have been or will be routed over them. Also, auto-routers typically do not solve the problem of routing specific signal return paths, and only typically route signal paths over and/or between pre-designated power planes or power plane regions.
It is therefore desirable to provide a design methodology and computer program that maintain proper reference returns for critical signal paths. It is also desirable to provide such a design methodology and computer program that optimize placement of signal paths and signal return paths during routing of an interconnect structure. It is further desirable to provide such a design methodology and computer program that auto-route signal paths while maintaining a proper reference returns for critical signal paths.